Mild detonating fuse end termination

ABSTRACT

The end of a mild detonating fuse is sealed within an adjacent metal ferrule by simple mechanical means and a hermetic seal is produced without using adhesives, soldering or any alien additives. The fuse is sealed by axial compressive forces which cause the fuse to conform to the shape of the metal ferrule adacent its end, thus expanding the end of the fuse into intimate contact with the metal ferrule to create an enlarged (augmented) explosive column.

nlte States Patent [1 1 1 3,929,072

Zapf 1 1 Dec. 30, 1975 MILD DETONATING FUSE END 3,589,292 6/1971 Hanson et a1 102/27 TERMINATION 3,665,858 5/1972 Travor .4 102/27 3,678,853 7/1972 Kilmer v. 102/27 [75] Inventor: Donald C. Zapf, Ben Lomond, Calif. 3713 3 1/1973 Johnson et a1, 102/27 [73] Assignee: The United States of America as 22 :2 2 represented by the Secretary of the Navy Washington Primary ExaminerVerlin R. Pendegrass [22] Filed: Nov. 26, 1974 Attorney, Agent, or Firm-R. S. Sciascia; P. Schneider; 21 Appl. No.: 527,325 Sheehan 52 Us Cl [57] ABSTRACT 1 I I I h 102/27 R The end of a mild detonating fuse is sealed within an [51] Int. Cl. CO6C 5/08; CO6C 7/02 [58] Field of Search 102,27 R 27] 70 R ad acent metal ferrule by simple mechanical means and a hermetic seal is produced without using adhe- [56] References Cited sives, solderrng or any alien additives The fuse 1s sealed by axial compressive forces WhlCh cause the UNlTED STATES PATENTS fuse to conform to the shape of the metal ferrule ada- 3,241,489 3/1966 Andrew et a1. 102/27 cent its end, thus expanding the end of the fuse into l02/Z7 intimate contact with the metal ferrule to create an c imme 102/27 3,368,485 2/1968 Klotz 102/27 enlarged (augmented) exploswe column. 3,572,246 3/1971 Hare et a1. 102/27 3 Claims, 6 Drawing Figures US. Patent Dec.30, 1975 Sheet10f2 3,929,072

US. Patsnt Dec. 30, 1975 Sheet 2 of2 3,929,072

% HQM J ll v MILD DETONATING FUSE END TERMINATION BACKGROUND OF THE INVENTION The present invention relates generally to an end termination for a mild detonating fuse (MDF) and, more particularly to methods of attaching a MDF to a metal ferrule by a simple seating and trimming process.

Prior methods of attaching a MDF include soldering,

adhesives and crimping. Soldering and adhesion demand high operator skill levels and the processes are very difficult to inspect for quality. Crimping or swaging metal parts onto a MDF involves deformation of the MDF sheath is a radially inward direction which tends to reduce the diameter of the explosive core. Reduction of the core diameter tends to reduce the reliability of propagation of the core. Thus, there are inherent deficiencies in the foregoing known methods.

SUMMARY OF THE INVENTION The present method overcomes these deficiencies by a Seating process wherein an MDF is compressed axially and, as a result, diametrically expanded into a stepped bore in the metal to which it is effectively attached and sealed. The expansion into the stepped bore upsets the fuse creating an enlarged explosive column.

OBJECTS OF THE INVENTION BRIEF DESCRIPTION OF THE DRAWINGS Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings, in which:

FIG. 1 is a cross-sectional view of the MDF in an initial step of a method developed in accordance with the present invention for making the detonating fuse;

FIG. 2 is a cross-sectional view of the MDF at an intermediate step of said method;

FIG. 3 is a cross-sectional view of the MDF at a final step of the said method;

FIG. 4 is a cross-sectional view of the MDF at an initial step of a second method developed in accordance with the present invention for making the detonating fuse;

FIG. 5 is a cross-sectional view of the MDF at an intermediate step of the second method; and

FIG. 6 is a cross-sectional view of the MDF at a final step of the second method.

Throughout the drawings like numerals indicate the same parts.

DETAILED DESCRIPTION OF THE INVENTION FIG. 1 shows an MDF 10 which is positioned within the bore 11 of a metal ferrule or socket 12. The fuse 10 is commercially obtainable under the name of MDF, while the ferrule 12 may consist of any electrically conducting metal such as stainless steel commonly used to connect an MDF to a supplemental explosive. A clamp 14 holds the MDF in its proper position within the bore ofthe ferrule 12. The clamp 14 may have optional plastic tubing 13 located at its gripping surface to assist the grip. A metal ram 16 applies the required axial compressive forces to seat the MDF 10 within the bore of the ferrule 12, while guide 18 insures that the ram 16 and MDF remain axially aligned so that end 19 of MDF l0 interfaces with the adjacent end of the ram 16. It should be noted that the only space available for the fuse 10 to expand, under the compressive forces of the ram, is the conical portion 20 and cylindrical portion 22 forming the interior seat of the socket or ferrule 12.

In FIG. 2 the MDF has been upset or deformed by the compressive forces and tools (clamp 14, guide 18 and ram 16) are shown removed. As can be seen in FIG. 2, the portion of the fuse l0 nearest its end 19 is deformed to conside with the shape of the counterbore of the metal ferrule 12.

The result of the next step is shown in FIG. 3. The end of the MDF is machined to provide an expanded explosive core 26, with the MDF l0 and ferrule 12 forced into such intimate contact that an airtight seal is formed. It is also possible to machine the end of the ferrule so that the ends of the ferrule 12 and the fuse 10 are flush, such as shown in FIG. 6.

The first step of a second method of fabrication, as shown in FIG. 4, is similar to first step (FIG. 1) of the foregoing method. That is, an MDF 30 is inserted through the bore 31 of a metal ferrule 32 so that is end 34 is located within an enlarged portion 36 of the bore 31. The fuse 30 is gripped by a clamp 38 and a ram 40 is used to apply the axial force to the fuse. As before, optional plastic tubing 42 may be included on the gripping surface of the clamp 38 to assist in forming a tight gripping contact with the MDF 30. Guide 44 insures axial alignment between the fuse 30 and the ram 40.

In FIG. 5 the MDF has been compressed so that it is radially enlarged to conform to the shape of the inner bores of both the ferrule 32 and the guide 44, causing the compressed end 46 of the fuse 30 to extend out beyound the end 48 of the ferrule 32. In FIG. 5, the MDF 30 has already been ejected from the guide (not shown).

FIG. 6 demonstrates the appearance of the fuse 30 and guide 32 after the end 46 of the fuse 30 has been machined flush with the end 48 of the ferrule 32.

Initial testing of the invention concentrated with method 1, where the MDF is seated within the counterbore in the ferrule, and both the MDF and the ferrule machined back to clean the face. Experimentation with approximately 65 units, some of which were sectioned to examine to the degree of counterbore filling, and some of which were tested for leakage, determined that method 1 was practicable. This method produced a mechanical attachment stronger than the MDF and a hermetic seal better than 10 cc/sec. On the other hand, no deleterious effects were created on the explosive core.

With respect to the second method, testing was conducted on 12 units and the force applied to the upsetting ram was increased in steps. The units were examined externally; some were sectioned and some were tested for leakage through the joint. It was determined that, for 0.073 nominal diameter MDF (99.99 pure aluminum sheath), it was necessary to impose loads in excess of 120 pounds to get leakage less than lXlO cc/sec, and loads of 200 pounds to be certain that the MDF expanded to fill the counterbore completely. It also became evident that a good deal of the applied force is resisted by friction of the upset MDF on the walls of the guide, and that the length of the MDF in contact with the walls of the guide must be controlled to assure reproducible results.

Accordingly, a series of trials were conducted the limits of control required and to attempt to establish a sound technique which would produce reproducible results. The force and the amount of protrusion of the MDF before seating were varied. The units were examined externally and in section, with leak testing where advisable. Prior to the start of this series it was determined that at least 0.030 inches of MDF should protrude from the ferrule after sealing, since the disturbance created on the very end by the ramming operation extends that far and should be trimmed off. The amount protruding after seating appeared to be governed by the amount protruding before seating and by the seating force value.

Results of this series were that the leakage was acceptably low at 140 pounds of seating force or greater. Complete filling of the ferrule counterbore occurred at forces of 200 pounds or more, confirming previous experience. The best results were obtained in the range of 220 to 260 pounds, however due to equipment problems the 220 pound value is in question, suspected to be closer to 240 pounds. It is thus reasonably safe to conclude that seating force of 250 i 10 pounds is effective. It also appears that a pre-seating protrusion of the MDF of 0.100 t 0.010 inches produces suitable postseating protrusions.

These values were employed in the preparation of 18 units which were used as donors in explosive train testing, with complete success.

Thus, two methods have been described and shown for seating the end of an MDF within a ferrule or socket both of which result in a mechanical attachment stronger than the MDF and a hermetic seal better than 10 cc/sec, obtained without the aid of adhesives, soldering or any other additives, and which do not create deterious effects on the explosive core.

Obviously, many modifications and variations of the present invention are possible in light of the above teachings. It is therefore to be understood that, within the scope of the appended claims, the invention may be practiced otherwise than as specifically described.

What is claimed is:

l. A method of seating a mild detonating fuse within a metal ferrule having a small bore portion corresponding to the diameter of said fuse and linearly adjacent thereto and a coaxial enlarged bore portion with a diameter larger than the diameter of said fuse, said method comprising:

positioning said fuse within the bore portions of said ferrule so that the end of said fuse is located within said enlarged bore portion; gripping said fuse to prevent axial movement; applying axial forces to said end of said fuse to compress said fuse causing it to conform to the shape of said enlarged bore portion of said ferrule; and

machining said compressed end of said fuse to produce a flat clean surface.

2. The method of claim 1 wherein said step of machining said end of said fuse also includes machining the end of said ferrule so that the ends of said fuse and said ferrule are flush.

3. A method of sealing a mild detonating fuse within a metal ferrule having a small bore portion and a coaxial enlarged bore portion, said method comprising:

positioning said fuse within said bores so that the end of said fuse extends out beyond the end of said enlarged bore portion;

providing a removable extension of said enlarged bore immediately adjacent said end of said enlarged bore;

gripping said fuse to prevent axial movement;

applying axial forces to said end of said fuse to compress said fuse causing it to conform to the shape of said enlarged bore;

removing said extension of said enlarged bore;

machining said end of said compressed fuse to make it flush with the end of said enlarged bore to thereby produce a clean flat surface. 

1. A method of seating a mild detonating fuse within a metal ferrule having a small bore portion corresponding to the diameter of said fuse and linearly adjacent thereto and a coaxial enlarged bore portion with a diameter larger than the diameter of said fuse, said method comprising: positioning said fuse within the bore portions of said ferrule so that the end of said fuse is located within said enlarged bore portion; gripping said fuse to prevent axial movement; applying axial forces to said end of said fuse to compress said fuse causing it to conform to the shape of said enlarged bore portion of said ferrule; and machining said compressed end of said fuse to produce a flat clean surface.
 2. The method of claim 1 wherein said step of machining said end of said fuse also includes machining the end of said ferrule so that the ends of said fuse and said ferrule are flush.
 3. A method of sealing a mild detonating fuse within a metal ferrule having a small bore portion and a coaxial enlarged bore portion, said method comprising: positioning said fuse within said bores so that the end of said fuse extends out beyond the end of said enlarged bore portion; providing a removable extension of said enlarged bore immediately adjacent said end of said enlarged bore; gripping said fuse to prevent axial movement; applying axial forces to said end of said fuse to compress said fuse causing it to conform to the shape of said enlarged bore; removing said extension of said enlarged bore; machiNing said end of said compressed fuse to make it flush with the end of said enlarged bore to thereby produce a clean flat surface. 